Control device for a flow of fluid

ABSTRACT

The invention relates to a device comprising at least one safety shut-off control valve. A safety valve is optionally connected to said safety shut-off control valve, connected in series in the fluid flow path. In the safety shut-off control valve, a sealing valve is returned to a sealing position against a seat by means of a return spring, and is controlled by a linear actuator and a connecting rod for continuous adjustment of the valve opening. The connecting rod comprises two independent segments which are at least partially made from a ferromagnetic material and which are magnetically coupled to a magnetic coupling circuit that is activated by a coil. While electric power is being supplied to the coil, the magnetic field that said coil creates maintains the linking rod segments coupled to one another, such that the linear actuator can control the sealing valve. Once the power being supplied to the operating coil is interrupted, the segments separate and the sealing valve returns to said sealing position regardless of the position of the linear actuator. At the same time, the check valve of the safety valve is pushed back to the sealing position by a return spring. In this way, a continuous control valve with a double safety system is produced.

This application is a U.S. national phase application of PCTInternational Application No. PCT/FRO2/00796 filed Mar. 6, 2002.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to electromagnetic valves for controllinga fluid flowrate in a fluid circulation path.

Such valves are used in particular to adjust the gas flowrate feeding agas burner or boiler.

Already known in the art are solenoid valves for continuous adjustmentof the gas flowrate by means of a sealing valve moving axially andcooperating with a seat to determine in the gas passage a gas passagesection that is adjustable between a fully open position and a minimumopen position. As a general rule, solenoid valves enabling continuousadjustment of the gas flowrate do not provide an adjustment going as faras total shut-off, and a shut-off valve must be associated with them.

There is also known, for adjusting the gas flowrate, a technologyemploying a plurality of valves connected in parallel and each passing aportion of the maximum gas flowrate. In this case, each solenoid valvecan totally shut off its own passage, closure of all of the valvescompletely shutting off the gas passage. The drawback is discontinuousadjustment of the gas flowrate, each solenoid valve defining anadjustment plateau.

In all cases, the standards currently in force governing the control ofgas flows impose the provision of two safety systems in series, oneafter the other, to ensure safe shut-off in the event of failure of theelectrical power supply to the solenoid valve.

In the technology employing a plurality of valves connected in parallel,it is therefore necessary to add a safety solenoid valve in series withthe set of parallel solenoid valves.

In the continuous adjustment solenoid valve technology, where thecontinuous adjustment solenoid valve is associated with a total shut-offsolenoid valve, it is also necessary to add a safety solenoid valve toensure double shut-off in the event of failure of the electrical powersupply.

Clearly the systems referred to above make the device very complicated,necessitating the simultaneous use of a plurality of solenoid valves andtheir control circuits.

There is also known, from the document DE 18 06 094 B, a double safetysolenoid valve operating in on/off mode. In the above document, thesealing valve is mounted at the end of a tubular body in which slides anactuator rod fastened to a drive magnetic core. The drive magnetic coreis driven by a drive coil which generates a magnetic field causing axialmovement of the magnetic drive core. A failsafe second magnetic core canmove axially relative to the first drive magnetic core, from which it isseparated by a non-magnetic ring. The failsafe second magnetic core isspring-loaded in the direction of the sealing valve, and is magneticallydriven by a failsafe second coil which generates a magnetic fieldcausing axial movement of the failsafe second core. The sealing valve isurged by a spring toward the valve seat. A device of this kind does notprovide continuous adjustment of the position of the sealing valvefacing the seat: the valve operates in on/off mode, the sealing valvebeing able to assume only a fully open position and a closed position,according to the state of energization of the coils. Also, the drivemagnetic core is not fastened to the sealing valve, but is connected tothe sealing valve by a rod sliding in a cylindrical body which isfastened to the sealing valve. Further, to open the valve, it isnecessary to generate a strong magnetic field to cause the magneticcores to stick to each other, which necessitates powerful and bulkycoils.

SUMMARY OF THE INVENTION

The problem addressed by the present invention is that of ensuring, atone and the same time, firstly continuous adjustment of the fluidflowrate in a fluid circulation path, and secondly safe shut-off in theevent of failure of the electrical power supply to the solenoid valves,and of achieving this using a small number of solenoid valves andcontrol circuits, to simplify the device and reduce its cost.

Another problem that certain embodiments of the invention aim to solveis that of controlling the adjustment solenoid valve by means of amotor, for continuous and accurate adjustment, whilst ensuring automaticreturn of the motor to the solenoid valve shut-off position without riskof crushing or of amplification of the phenomenon of sticking of theseals and with no risk of slippage or jamming of the motor.

To achieve the above and other objects, the invention provides a controland safety device for a flow of fluid through a fluid circulation paththrough a main body of the device, which includes:

-   -   an axial displacement sealing valve cooperating with a seat to        determine, in the fluid passage, a fluid passage section        adjustable between a fully open position and a shut-off        position,    -   a linear actuator directly mechanically connected to the sealing        valve by an axial displacement connecting rod for continuously        and axially moving the sealing valve facing the seat between its        fully open and shut-off positions, enabling continuous        adjustment of the position of the sealing valve facing the seat;

according to the invention:

-   -   the connecting rod includes a first segment and a second segment        which are coaxial and independent, the first segment being        fastened to, or integral with, the sealing valve, the second        segment being driven by the linear actuator, and the two        segments being able to move axially relative to each other        between a relatively close together position and a relatively        far apart position relative to the airgap,    -   each of the first and second segments of the connecting rod        comprises at least one respective ferromagnetic material        connecting portion, two respective contact surfaces of the two        connecting portions facing each other,    -   a return spring urges the sealing valve and the first segment of        the connecting rod away from the second segment of the        connecting rod to spring-load the sealing valve into the        shut-off position,    -   a magnetic coupling circuit with an excitation coil is        magnetically coupled to the connecting portions of the segments        of the connecting rod and is shaped to generate selectively a        magnetic field circulating between the two connecting portions        of the segments of the connecting rod, said magnetic field        causing mutual magnetic attraction of the segments of the        connecting rod toward each other against a return force exerted        by the return spring, said magnetic attraction being greater        than the return force of the return spring when the two segments        are in the relatively close together position.

Thus supplying power to the excitation coil causes the connecting rodsegments to stick to each other, ensuring mechanical coupling of thesealing valve to the linear actuator for its functional movements, andinterrupting the power supply to the excitation coil causes theconnecting rod segments to be released from each other, ensuringdecoupling of the sealing valve, which is then returned to the shut-offposition by the return spring, regardless of the status of the linearactuator.

In the description and the claims, the expression “linear actuator”designates any member for moving the sealing valve axially andcontinuously to and maintaining it in any position between the fullyopen and closed limit positions, a member of this kind remaining fixedin position in the event of interruption of the electrical power supply.One example of this kind of linear actuator is a rotary motor associatedwith a screw jack.

According to one option, the connecting portions of the segments of theconnecting rod have respective plane contact surfaces.

Alternatively, the connecting portions of the segments of the connectingrod have respective corresponding frustoconical contact surfaces.

The linear actuator preferably includes a motor, for example a steppermotor.

One advantageous embodiment of the device includes:

-   -   a sensor responsive to the electrical current flowing in the        excitation coil and generating an electrical coupling signal in        the event of closure of the magnetic coupling circuit by        movement toward each other and sticking of the segments of the        connecting rod to each other, and    -   a control circuit of the linear actuator, receiving the        electrical coupling signal, and adapted to interrupt the        energization of the linear actuator in the closure direction on        receiving said electrical coupling signal.

In this way, regardless of the position of the linear actuator at thetime of interruption of the electrical power supply, the linear actuatorthen returns to a perfectly defined closure position without causingexcessive clamping of the sealing valve onto the seat. The closureposition of the linear actuator is defined accurately and reproducibly.This avoids all risk of the motor of the linear actuator jamming, aswould occur in the event of excessive compression of the sealing valveonto the seat.

In a first simplified embodiment the magnetic coupling circuit and theexcitation coil are components of the main body of the device, theassembly constituting a safety shut-off proportional control valve inthe event of absence of the electrical power supply.

In this case, the device according to the invention must, to comply withsafety standards, further been associated with a safety valve with asafety sealing valve carried by a mobile magnetic core spring-loaded bya return spring into a shut-off position and acted on by a valve openingmagnetic field generated by a safety valve magnetic circuit and anactuation coil, the safety valve being connected in series in the fluidcirculation path, the safety valve actuation coil being electricallyenergized simultaneously with the excitation coil of the safety shut-offcontrol valve.

A second embodiment of the device according to the invention furtherincludes a safety valve with a safety sealing valve carried by a mobilemagnetic core spring-loaded by a return spring into a shut-off positionand acted on by a valve opening magnetic field generated by a safetyvalve magnetic circuit and an actuation coil, the safety valve beingconnected in series in the fluid circulation path, the safety valvemagnetic circuit being formed to constitute simultaneously the magneticcoupling circuit of the safety shut-off control valve, and the actuationcoil simultaneously fulfilling the function of excitation coil of thesafety shut-off control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willemerge from the following description of particular embodiments, givenwith reference to the accompanying figures, in which:

FIG. 1 is a diagrammatic view in section of a first embodiment of afluid flowrate control and safety device in accordance with the presentinvention, shown in a shut-off position;

FIG. 2 is a diagrammatic view in section of the FIG. 1 device, in aregulation position;

FIG. 3 is a diagrammatic view in section of the FIG. 1 device in ashut-off position in the event of interruption of the electrical powersupply;

FIG. 4 is a diagrammatic view in section of a second embodiment of afluid flowrate control and safety device in accordance with the presentinvention, shown in a fully shut-off position;

FIG. 5 is a view in section of the FIG. 4 device with the safetysolenoid valve open and the adjustment solenoid valve closed;

FIG. 6 is a diagrammatic view in section of the FIG. 4 device in aflowrate regulation position; and

FIG. 7 is a diagrammatic view in section of the FIG. 4 device in adouble safety shut-off position in the event of interruption of theelectrical power supply.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment shown in FIGS. 1 to 3, the fluid flowrate control andsafety device provides firstly the function of continuous adjustment ofthe fluid flowrate, and secondly the function of automatic shut-off inthe event of absence of the electrical power supply to the device.

The device comprises a main body 1 in which a fluid circulation path isprovided between an inlet 2 and an outlet 3. In the embodiment shown inFIG. 1, the fluid path passes through the inlet 2, and then an upstreamchamber 4, a downstream chamber 5, an outlet chamber 6, and finally theoutlet 3.

Between the upstream chamber 4 and the downstream chamber 5, a sealingvalve 7 moves axially along the axis I—I and cooperates with a seat 8 todetermine, in the fluid passage, a fluid passage segment that isadjustable between a fully open position and a shut-off position. FIG. 1shows the shut-off position.

The sealing valve 7 is directly mechanically connected to a linearactuator 10 by a connecting rod 9. The linear actuator 10 is adapted tomove axially the connecting rod 9 and the sealing valve 7 between thefully open position and the shut-off position, and to retain them in anychosen adjustment position between the extreme positions. The linearactuator 10 can comprise an electric motor, for example, supplied withpower via a control circuit 11.

The connecting rod 9 is in two separate parts, comprising independentfirst and second coaxial segments 12 and 13. The first segment 12 isfastened to, or integral with, the sealing valve 7. The second segment13 is driven by the linear actuator 10. By sliding in the main body 1along the axis I—I, the two segments 12 and 13 can move axially relativeto each other between a relatively close together position (FIG. 1) anda relatively far apart position (FIG. 3).

The first segment 12 of the connecting rod 9 includes at least oneferromagnetic material connecting portion 14. Similarly, the secondsegment 13 of the connecting rod 9 includes a ferromagnetic materialconnecting portion 15. The two connecting portions 14 and 15 haverespective contact surfaces 16 and 17 facing each other.

A return spring 18 urges the sealing valve 7 and the first segment 12 ofthe connecting rod 9 in the direction of the seat 8, i.e. away from thesecond segment 13 of the connecting rod 9, to the point where thesolenoid valve is shut-off.

A magnetic coupling circuit 19 with an excitation coil 20 ismagnetically coupled to the connecting portions 14 and 15 of thesegments 12 and 13 of the connecting rod 9. The magnetic couplingcircuit 19 is shaped to generate selectively a magnetic fieldcirculating between the two connecting portions 14 and 15 of thesegments 12 and 13. FIG. 1 shows that the excitation coil 20 is anannular coil around the ferromagnetic material connecting portions 14and 15 of the connecting rod 9. The C-shaped magnetic coupling circuit19 closes the field lines externally of the excitation coil 20 betweenthe two connecting portions 14 and 15, leaving only a narrow airgapbetween the distal pole 19 a and the proximal pole 19 b of the magneticcoupling circuit 19, on the one hand, and the respective connectingportions 14 and 15 of the connecting rod 9, on the other hand. There isa third airgap E at the interface between the respective contactsurfaces 16 and 17 of the connecting portions 14 and 15 of theconnecting rod 9, shown more clearly in FIG. 3 in the relatively farapart position.

The excitation coil 20 is supplied with electrical current via inputconductors 21. When an electric current is present, the excitation coil20 creates a magnetic field which flows in the magnetic coupling circuit19 and the connecting portions 14 and 15 to cause mutual magneticattraction of the segments 12 and 13 of the connecting rod 9 toward eachother against a return force exerted by the return spring 18. Theexcitation coil 20 and its excitation current are chosen so that themagnetic attraction exerted between the two segments 12 and 13 of theconnecting rod 9 in the relatively close together position is greaterthan the return force of the return spring 18.

As a result, supplying the excitation coil 20 with electrical energymaintains the sticking together of the segments 12 and 13 of theconnecting rod 9, assuring permanent mechanical coupling of the sealingvalve 7 to the linear actuator 10 in the event of longitudinal movementsto adjust the fluid flowrate.

Clearly, when the segments 12 and 13 are in the relatively far apartposition relative to the airgap E, the magnetic flux generated by theexcitation coil 20 is lower because of the presence of the airgap, andit would then be necessary to use a high power excitation coil 20 if theenergization of the excitation coil 20 to assure mutual magneticattraction of the segments 12 and 13 were required to be greater thanthe return force exerted by the return spring 18. The volume of thedevice would then be greatly increased, and the production cost would behigher, as would be the consumption of energy to energize the coil.

According to the invention, it is preferred to use a lower power coil,of just sufficient power to keep the segments 12 and 13 stuck to eachother when they are in the close together position, the magneticattraction becoming insufficient to move the segments 12 and 13 towardeach other when the airgap E is present. Thanks to the presence of thelinear actuator, which can move the segments 12 and 13 relative to eachother to bring them into contact with each other after the electricalpower supply is restored, the device can then be returned to a state ofcontinuous mechanical connection between the linear actuator and thesealing valve by energization of the excitation coil 20.

The operation of the device is explained further with reference to FIGS.1 to 3.

In FIG. 1, the device is in a permanently shut-off position: the sealingvalve 7 bears on the seat 8 to shut off totally the fluid circulationpath between the upstream chamber 4 and the downstream chamber 5. Thesealing valve 7 is held in this position by the first segment 12 of theconnecting rod 9, which is itself pushed by the spring 18 and by thesecond segment 13, which is itself loaded by the linear actuator 10. Thedevice retains this state regardless of the energization of theexcitation coil 20.

FIG. 2 shows the device in the state of normal fluid flowrate regulationoperation: the excitation coil 20 is supplied with electrical currentand causes the segments 12 and 13 of the connecting rod 9 to stickpermanently to each other. In this case, the linear actuator 10 can moveaxially along the longitudinal axis I—I of the connecting rod 9 and thesealing valve 7 relative to the seat 8, to adjust continuously the fluidpassage section 71 that determines the fluid flowrate in the fluidcirculation path. The sealing valve 7 remains coupled to the linearactuator 10 for as long as the excitation coil 20 is energized.

If the supply of electrical power to the excitation coil 20 isinterrupted, the device assumes the state shown in FIG. 3 because of thedisconnection of the electrical power supply from the excitation coil20, the magnetic field in the magnetic coupling circuit 19 disappears,as a result of which the magnetic attraction between the segments 12 and13 of the connecting rod 9 disappears. The second segment 13 remainsfixed, its position being determined by the linear actuator 10, which isalso fixed because of the absence of electrical power. On the otherhand, the first segment 12 is moved by the return spring 18 toward theshut-off position, with the result that the sealing valve 7automatically comes to bear again on the seat 8, totally shutting offthe solenoid valve.

In this FIG. 3 position, the large third airgap E separates the twosegments 12 and 13 when the power supply is interrupted with the linearactuator 10 in the fully or partially open position. The segments 12 and13 are therefore in a relatively far apart position relative to theairgap E.

When the electrical power supply is restored, because of the thirdairgap E, the magnetic field generated by the excitation coil 20 isinsufficient for the magnetic attraction to overcome the return force ofthe return spring 18 and cause the segments 12 and 13 to stick to eachother. The linear actuator 10 must move the second segment 13 in thedirection of the first segment 12, moving the contact surfaces 16 and 17toward each other, until the third airgap E has been reducedsufficiently and the segments 12 and 13 stick to each other. Thesolenoid valve then resumes its function of fluid flowrate regulation.

FIG. 1 also shows means for automatically commanding stopping of thelinear actuator 10 when it returns to the shut-off position, after theelectrical power supply is restored. As a matter of fact, from thesafety shut-off position shown in FIG. 3, in which the actuator holdsthe second segment 13 of the connecting rod 9 retracted from the firstsegment 12 of the connecting rod 9, which is pushed into the shut-offposition by the return spring 18, when the electrical power supply isrestored it is necessary to control the linear actuator 10 so that itmoves the contact surfaces 16 and 17 toward each other, with asufficiently small distance between them for the magnetic field again tocause the segments 12 and 13 of the connecting rod 9 to stick together.However, it is necessary at the same time to control the stopping of thelinear actuator 10 as soon as this sticking is achieved, failing whichthe linear actuator 10 continues to move and presses the connecting rod9 and the sealing valve 7 against the seat 8, crushing seals such as theseal 70. Also, if the linear actuator 10 is not stopped when sticking isachieved, the linear actuator 10 can slip and lose its positionalregistration, which degrades the accuracy of subsequent openingadjustments of the sealing valve 7.

The FIG. 1 embodiment interrupts the supply of power to the actuator assoon as the coupling between the two segments 12 and 13 of theconnecting rod 9 is obtained.

To this end, a sensor 22 responsive to the electrical current flowing inthe excitation coil 20 is inserted into the input conductors 21supplying power to the excitation coil 20; it generates at its output 23an electrical coupling signal when the magnetic coupling circuit 19 isclosed by movement toward each other and sticking together of thesegments 12 and 13 of the connecting rod 9. The output 23 of the sensor22 is connected to an input 24 of the control circuit 11. Thus thecontrol circuit 11 of the linear actuator 10 receives the electricalcoupling signal and is adapted to interrupt the supply of power to thelinear actuator 10 in the direction of closure of the sealing valve 7 onreceiving said electrical coupling signal.

In the embodiment shown in FIGS. 1 to 3, the magnetic coupling circuit19 and the excitation coil 20 are members fitted to the main body 1 ofthe device, the assembly constituting a control valve with safetyshut-off in the event of absence of the electrical power supply.

To satisfy applicable safety standards, the safety shut-off controlvalve shown in FIGS. 1 to 3 can be associated with a safety valve of anytype known to the person skilled in the art, connected in series in thefluid flow path.

For example, said safety shut-off valve can be associated with a safetyvalve having a sealing valve carried by a mobile magnetic corespring-loaded by a return spring into a shut-off position and acted onby a valve opening magnetic field generated by a magnetic circuit and anactuation coil. In this case, the actuation coil of the safety valve issupplied with electrical power at the same time as the excitation coil20 of the device shown in FIGS. 1 to 3.

Nevertheless, the embodiment shown in FIGS. 4 to 7 may be preferred asit duplicates control valve safety.

In this embodiment, a safety shut-off control valve A, shown in theright-hand half of FIG. 4, is associated with a safety valve B, shown inthe left-hand half of FIG. 4.

The safety shut-off control valve A has the same structure as the firstembodiment shown in FIGS. 1 to 3. It therefore includes the samecomponents, identified by the same reference numbers, including inparticular: the main body 1, the inlet 2, the outlet 3, the upstreamchamber 4, the downstream chamber 5, the outlet chamber 6, the sealingvalve 7, the seat 8, the connecting rod 9, the linear actuator 10, thefirst segment 12 of the connecting rod 9, the second segment 13 of theconnecting rod 9, the ferromagnetic material connecting portions 14 and15, the return spring 18, and the magnetic coupling circuit 19 with itsdistal pole 19 a and its proximal pole 19 b.

In the embodiment shown in FIGS. 4 to 7, the safety shut-off controlvalve A differs in terms of the structure of the magnetic couplingcircuit 19 and the excitation coil generating the magnetic field in themagnetic coupling circuit 19, in the manner explained hereinafter.

The safety valve B is provided in the same main body 1, and is connectedin series into the fluid circulation path between a main inlet 25 andthe inlet 2 of the safety shut-off control valve A. The safety valve Bincludes a safety sealing valve 26 carried by a mobile magnetic core 27which can slide in the main body 1 along a longitudinal axis II—II tomove the safety sealing valve 26 between a shut-off position, shown inFIG. 4, in which it bears on a safety seat 28 to oppose any passage offluid, and an open position shown in FIGS. 5 and 6, in which it isretracted from the safety seat 28 to allow the fluid to flow from themain inlet 25 to the inlet 2 of the safety shut-off control valve A.

The mobile magnetic core 27 is spring-loaded by a return spring 29toward a shut-off position.

The mobile magnetic core 27 is associated with a fixed magnetic core 30,disposed coaxially along the axis II—II, and from which it is separatedby an airgap 31. An actuation coil 32, supplied with power by anelectrical power supply, is disposed around the magnetic cores 27 and30.

The magnetic coupling circuit 19 comprises, starting from the distalpole 19 a, a distal plate 119 a, a portion of which is in the vicinityof the mobile magnetic core 27 in order to couple it magnetically tosaid mobile magnetic core 27. Similarly, the magnetic coupling circuit19 includes, starting from the proximal pole 19 b, a proximal plate 119b, a portion of which is in the vicinity of the fixed magnetic core 30for the purpose of securing its magnetic coupling. The magnetic fieldgenerated by the actuation coil 32 therefore causes mutual attraction ofthe fixed magnetic core 30 and the mobile magnetic core 27, whichattraction tends to reduce the airgap 31 and to cause the two cores 27and 30 to stick to each other to open the safety valve B.Simultaneously, the magnetic field generated by the actuation coil 32propagates in the magnetic coupling circuit 19 as far as the poles 19 aand 19 b, and then in the connecting portions 14 and 15 of theconnecting rod 9 to cause the segments 12 and 13 of the connecting rod 9to stick together, enabling the linear actuator 10 to control the safetyshut-off control valve A.

As a result, the magnetic circuit of the safety valve B is shaped toconstitute simultaneously the magnetic coupling circuit 19 of the safetyshut-off control valve A, and the actuation coil 32 simultaneouslyfulfils the function of the excitation coil of the safety shut-offcontrol valve A.

The operation of the device is explained further with reference to FIGS.4 to 7.

In FIG. 4, the device is in a safety closure position: the safetyshut-off control valve A is in the fully shut-off position, with thesealing valve 7 bearing against the seat 8. Similarly, the safety valveB is in the shut-off position, the actuation coil is not energized, sothat the safety sealing valve 26 and the mobile magnetic core 27 arepushed back by the return spring 29, which presses the safety sealingvalve 26 against the safety seat 28.

In FIG. 5, the actuation coil 32 is energized, which causes the mobilemagnetic core 27 to be attracted by the fixed magnetic core 30 andretracts the safety sealing valve 26 from the safety seat 28 to open thefluid passage. However, the fluid passage continues to be shut off bythe safety shut-off control valve A, the linear actuator 10 of which hasnot yet been opened.

In FIG. 6, the device is in the regulation state: the actuation coil 32being supplied with electrical current, it produces a magnetic fieldwhich simultaneously opens the safety valve B and causes the segments 12and 13 of the connecting rod 9 to stick together, the linear actuator 10efficiently moving the sealing valve 7 relative to the seat 8 at will toadjust the fluid passage section 71.

Starting from the regulation position shown in FIG. 6, if the supply ofpower to the actuation coil 32 is interrupted, the device assumes thesafety closure state shown in FIG. 7: when the magnetic field in themagnetic coupling circuit 19 disappears, the mobile magnetic core 27 andthe safety sealing valve 26 are pushed back by the return spring 29 to aclosed position, to provide a first safety closure; simultaneously, thedisappearance of the magnetic field in the magnetic coupling circuit 19causes the first segment 12 of the connecting rod 9 to separate from thesecond segment 13, with a result that the first segment 12 of theconnecting rod 9 and the sealing valve 7 are pushed back by the returnspring 18 to a shut-off position against the seat 8, to provideautomatically a second safety closure.

When the power supply of the actuation coil 32 is restored, the safetyvalve B opens, but the safety shut-off control valve A remains closeduntil an operator or an appropriate program causes the linear actuator10 to operate in the direction that moves the segments 12 and 13 of theconnecting rod 9 toward each other, to stick the two segments together,and then in the direction that opens the safety shut-off control valveA.

Clearly this second embodiment is particularly economical for providinga double safety shut-off control valve.

As shown in FIGS. 4 to 7, the airgap 31 between the mobile magnetic core27 and the fixed magnetic core 30 is frustoconical in shape. This shapefacilitates attraction of the mobile magnetic core 27 over a longtravel. On the other hand, as seen better in FIG. 3, the third airgap Ebetween the segments 12 and 13 of the connecting rod 9 is limited by twoplane contact surfaces 16 and 17, because the traction between the twosegments 12 and 13 does not in principle need to be provided over a longtravel. Nevertheless, alternatively, respective correspondingfrustoconical contact surfaces 16 and 17 could be provided, in the sameway as for the airgap 31.

The present invention is not limited to the embodiments explicitlydescribed but includes variants and generalizations thereof within thescope of the following claims.

1. A control and safety device for a flow of fluid through a fluidcirculation path through a main body of the device, which includes: anaxial displacement sealing valve cooperating with a seat to determine,in the fluid passage, a fluid passage section adjustable between a fullyopen position and a shut-off position, a linear actuator directlymechanically connected to the sealing valve by an axial displacementconnecting rod, for continuously and axially moving the sealing valvefacing the seat between its fully open and shut-off positions, enablingcontinuous adjustment of the position of the sealing valve facing theseat, wherein: the connecting rod includes a first segment and a secondsegment which are coaxial and independent, the first segment beingintegral with the sealing valve, the second segment being driven by thelinear actuator, and the two segments being able to move axiallyrelative to each other between a relatively close together position anda relatively far apart position relative to an airgap, each of the firstand second segments of the connecting rod comprises at least onerespective ferromagnetic material connecting portion, two respectivecontact surfaces of the two connecting portions facing each other, areturn spring urges the sealing valve and the first segment of theconnecting rod away from the second segment of the connecting rod tospring-load the sealing valve into the shut-off position, a magneticcoupling circuit with an excitation coil is magnetically coupled to theconnecting portions of the segments of the connecting rod and is shapedto generate selectively a magnetic field circulating between the twoconnecting portions of the segments of the connecting rod, said magneticfield causing mutual magnetic attraction of the segments of theconnecting rod toward each other against a return force exerted by thereturn spring, said magnetic attraction being greater than the returnforce of the return spring when the two segments are in the relativelyclose together position, the magnetic coupling circuit and theexcitation coil are components of the main body of the device, with theresult that energization of the excitation coil maintains the magneticattraction of the segments of the connecting rod, ensuring themechanical coupling of the sealing valve to the linear actuator for itsfunctional movements, and interruption of the supply of power to theexcitation coil causes the segments of the connecting rod to be releasedfrom each other, ensuring the decoupling of the sealing valve, which isthen returned to the shut-off position by the return spring, regardlessof the status of the linear actuator.
 2. A device according to claim 1,wherein the connecting portions of the segments of the connecting rodhave respective plane contact surfaces.
 3. A device according to claim1, wherein the connecting portions of the segments of the connecting rodhave respective corresponding frustoconical contact surfaces.
 4. Adevice according to claim 1, wherein the linear actuator includes amotor.
 5. A device according to claim 1, further including: a sensorresponsive to the electrical current flowing in the excitation coil andgenerating an electrical coupling signal in the event of closure of themagnetic coupling circuit by movement toward each other and sticking ofthe segments of the connecting rod to each other, and a control circuitof the linear actuator, receiving the electrical coupling signal, andadapted to interrupt the energization of the linear actuator in theclosure direction on receiving said electrical coupling signal.
 6. Adevice according to claim 1, wherein the assembly comprising a safetyshut-off control valve in the event of absence of the electrical powersupply.
 7. A device according to claim 6, further comprising a safetyvalve with a safety sealing valve carried by a mobile magnetic corespring-loaded by a return spring into a shut-off position and acted onby a valve opening magnetic field generated by a safety valve magneticcircuit arid an actuation coil, and the safety valve being connected inseries in the fluid circulation path, the safety valve actuation coilbeing electrically energized simultaneously with the excitation coil ofthe safety shut-off control valve.
 8. A device according to claim 1,further including a safety valve with a safety sealing valve carried bya mobile magnetic core spring-loaded by a return spring into a shut-offposition and acted on by a valve opening magnetic field generated by asafety valve magnetic circuit and an actuation coil, the safety valvebeing connected in series in the fluid circulation path, the safetyvalve magnetic circuit being formed to constitute simultaneously themagnetic coupling circuit of the safety shut-off control valve, and theactuation coil simultaneously fulfilling the function of excitation coilof the safety shut-off control valve.
 9. A device according to claim 1,wherein the excitation coil and its excitation current are adapted to bejust sufficient to maintain the magnetic attraction of the segments toeach other when they are in the close together position.
 10. A deviceaccording to claim 1, wherein the magnetic coupling circuit comprises adistal pole and a proximal pole, leaving only a narrow airgap betweenthe distal pole and the proximal pole, and the respective connectingportions of the connecting rod.